1. Field of the Invention
This invention relates generally to packet data communication systems, and to a system and method for allocating fractional bandwidth in a fixed-frame communication system.
2. Background
Several systems are currently in place for connecting computer users to one another and to the Internet. For example, many companies such as Cisco Systems, provide data routers that route data from personal computers and computer networks to the Internet along conventional twisted pair wires and fiber optic lines. These same systems are also used to connect separate offices together in a wide area data network. However, these systems suffer significant disadvantages because of the time and expense required to lay high capacity communications cables between each office. This process is time consuming and expensive.
Many types of current wireless communication systems facilitate two-way communication between a plurality of subscriber radio stations or subscriber units (either fixed or portable) and a fixed network infrastructure. Exemplary communication systems include mobile cellular telephone systems, personal communication systems (PCS), and cordless telephones. The key objective of these wireless communication systems is to provide communication channels on demand between the plurality of subscriber units and their respective base stations in order to connect a subscriber unit user with the fixed network infrastructure (usually a wire-line system). In the wireless systems having multiple access schemes, a time xe2x80x9cframexe2x80x9d is used as the basic information transmission unit. Each frame is sub-divided into a plurality of time slots. Some time slots are used for control purposes and some for information transfer. Subscriber units typically communicate with a selected base station using a xe2x80x9cduplexingxe2x80x9d scheme thus allowing for the exchange of information in both directions of connection.
Transmissions from the base station to the subscriber unit are commonly referred to as xe2x80x9cdownlinkxe2x80x9d transmissions. Transmissions from the subscriber unit to the base station are commonly referred to as xe2x80x9cuplinkxe2x80x9d transmissions. Depending upon the design criteria of a given system, wireless communication systems have typically used either time division duplexing (TDD) or frequency division duplexing (FDD) methods to facilitate the exchange of information between the base station and the subscriber units. Both the TDD and FDD duplexing schemes are well known in the art.
Recently, wideband or xe2x80x9cbroadbandxe2x80x9d wireless communications networks have been proposed for the delivery of enhanced broadband services such as voice, data and video. The broadband wireless communication system facilitates two-way communication between a plurality of base stations and a plurality of fixed subscriber stations or Customer Premises Equipment (CPE).
Data communication systems often transfer data between the base station and the subscriber using fixed length data packets. One example of a fixed length data packet format is the Asynchronous Transfer Mode (ATM) data transfer protocol. ATM is described in xe2x80x9cHigh Performance Communication Networksxe2x80x9d by Jean Walrand and Pravin Varaiya, second edition(copyright) 2000 by Morgan Kaufmann Publishers, ISBN 1-55860-574-6, particularly in Chapter 6. ATM can satisfy a wide range of data communications needs, including highly variable data rates like Internet traffic, as well as time-sensitive traffic for voice or video connections. ATM provides flexibility by providing relatively small, fixed-length cells as the packets in which data is communicated.
ATM cells have a cell length of 53 bytes. 5 bytes of each cell are allocated to a header to be used for header information. Therefore, each ATM cell contains a payload section of 48 bytes.
The systems and methods of the present invention have several features, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention as expressed by the claims which follow, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled xe2x80x9cDetailed Description of the Inventionxe2x80x9d one will understand how the features of this invention provide several advantages over traditional allocation systems.
An aspect of the invention relates to a method and system for allocating bandwidth to constant bit rate connections with uplink needs known at the base station in a fixed-frame communication system, including calculating the integral cells per frame required at a connection, calculating the fractional cells per second required at the connection, setting a counter, adding the fractional cells per second to the counter, determining if the counter is above a preset limit, allocating an additional cell when the counter exceeds the preset limit, and reducing the counter a predetermined amount to reflect allocating the cell.
A further aspect of the invention relates to a wireless communication system including at least one base station and a plurality of subscriber stations. Each subscriber station has at least one subscriber with a connection between the subscriber and the subscriber station, wherein the subscriber station includes a controller with an allocation module. The allocation module includes a setup sub-module that calculates the fractional cells per second transmitted between the subscriber premises and the subscriber station, and a transmit sub-module that tracks the number of fractional cells per second and allocates a cell when the number of fractional cells per second reaches a predetermined level.